Playback apparatus and method, and recording medium

ABSTRACT

At a step S 2 , a defect period monitoring unit of a defect processing control unit stands by until the defect period monitoring unit detects the start of a defect period. When the defect period monitoring unit detects the start of a defect period, the processing proceeds to a step S 3 . At the step S 3 , defect period processing is performed. When the defect period monitoring unit detects the end of the defect period at a step S 4 , the processing proceeds to a step S 5 . At the step S 5 , post-defect period processing is performed.

BACKGROUND OF THE INVENTION

The present invention relates to an apparatus and a method for playbackand a recording medium, and particularly to an apparatus and a methodfor playback and a recording medium suitable for use in preventing amalfunction of a servo of an optical pickup resulting from a flaw or thelike on a disk medium, for example.

FIG. 1 shows a configuration of a conventional optical disk playbackapparatus for reproducing data recorded on an optical disk.

A spindle motor 2 in the conventional optical disk playback apparatusdrives and rotates an optical disk 1. An optical pickup 3 irradiates theoptical disk 1 with laser light, generates a signal corresponding to thereflected light, and then outputs the signal to an RF signal generatingunit 4, an FE signal generating unit 5, and a TE signal generating unit6. Also, the optical pickup 3 adjusts focus servo operation in responseto a focus drive signal from a focus driver 10, and adjusts trackingservo operation in response to a tracking drive signal from a trackingdriver 12.

The RF signal generating unit 4 generates an RF signal on the basis ofthe signal from the optical pickup 3, and then outputs the RF signal toa binarizing unit 7 and a defect detecting unit 8. The FE signalgenerating unit 5 generates a focus error signal (hereinafter describedas an FE signal) on the basis of the signal from the optical pickup 3,and then outputs the FE signal to a focus servo control unit 9. The TEsignal generating unit 6 generates a tracking error signal (hereinafterdescribed as a TE signal) on the basis of the signal from the opticalpickup 3, and then outputs the TE signal to a tracking servo controlunit 11.

The binarizing unit 7 generates a data signal by binarizing the RFsignal from the RF signal generating unit 4 into 0 or 1. The defectdetecting unit 8 detects a loss of a signal (defect) resulting from aflaw, a stain or the like present on the optical disk 1 on the basis ofthe RF signal from the RF signal generating unit 4, generates a defectsignal indicating a period of a defect detected, and then outputs thedefect signal to the focus servo control unit 9 and the tracking servocontrol unit 11.

A method for detecting a defect is, for example, to set level of thedefect signal during a period when level of the RF signal is lower thana predetermined threshold value as High, and to set the defect signalduring a period when the level of the RF signal is higher than thepredetermined threshold value as Low. Specifically, when the RF signalhas a level as shown in FIG. 2A, the defect signal has a correspondinglevel as shown in FIG. 2B.

During a normal period (period when the level of the defect signal fromthe defect detecting unit 8 is Low), the focus servo control unit 9generates a focus drive control signal corresponding to the FE signalfrom the FE signal generating unit 5, and then outputs the focus drivecontrol signal to the focus driver 10. When the level of the defectsignal is High, the focus servo control unit 9 holds level of the focusdrive control signal at a predetermined reference value or a value ofthe focus drive control signal immediately before the level of thedefect signal becomes High, as shown in FIG. 2D, and then outputs thelevel of the focus drive control signal to the focus driver 10.

The focus driver 10 generates a focus drive signal corresponding to thefocus drive control signal from the focus servo control unit 9, and thenoutputs the focus drive signal to the optical pickup 3.

During a normal period (period when the level of the defect signal fromthe defect detecting unit 8 is Low), the tracking servo control unit 11generates a tracking drive control signal on the basis of the TE signalfrom the TE signal generating unit 6, and then outputs the trackingdrive control signal to the tracking driver 12. When the level of thedefect signal is High, the tracking servo control unit 11 holds level ofthe tracking drive control signal at a predetermined reference value ora value of the tracking drive control signal immediately before thelevel of the defect signal becomes High, as shown in FIG. 2F, and thenoutputs the level of the tracking drive control signal to the trackingdriver 12.

The tracking driver 12 generates a tracking drive signal correspondingto the tracking drive control signal from the tracking servo controlunit 11, and then outputs the tracking drive signal to the opticalpickup 3.

In some cases, the conventional optical disk playback apparatus suppliesthe defect signal generated by the defect detecting unit 8 to the FEsignal generating unit 5 and the TE signal generating unit 6.

In such cases, during a normal period (period when the level of thedefect signal from the defect detecting unit 8 is Low), the FE signalgenerating unit 5 supplied with the defect signal generates the FEsignal on the basis of the signal from the optical pickup 3, and thenoutputs the FE signal to the focus servo control unit 9. When the levelof the defect signal is High, the FE signal generating unit 5 holdslevel of the FE signal at a predetermined reference value or a value ofthe FE signal immediately before the level of the defect signal becomesHigh, as shown in FIG. 2C, and then outputs the level of the FE signalto the focus servo control unit 9. The focus servo control unit 9outputs a focus drive signal as shown in FIG. 2D corresponding to the FEsignal whose level is being held constant.

During a normal period (period when the level of the defect signal fromthe defect detecting unit 8 is Low), the TE signal generating unit 6supplied with the defect signal generates the TE signal on the basis ofthe signal from the optical pickup 3, and then outputs the TE signal tothe tracking servo control unit 11. When the level of the defect signalis High, the TE signal generating unit 6 holds level of the TE signal ata predetermined reference value or a value of the TE signal immediatelybefore the level of the defect signal becomes High, as shown in FIG. 2E,and then outputs the level of the TE signal to the tracking servocontrol unit 11. The tracking servo control unit 11 outputs a trackingdrive signal as shown in FIG. 2F corresponding to the TE signal having afixed value.

Thus, even if normal reflected light is not obtained because of thepresence of a flaw or the like on the optical disk 1, the conventionaloptical disk playback apparatus thus formed holds the level of the focusdrive signal and the tracking drive signal while the level of the defectsignal is High. Therefore, a malfunction of a focus servo and a trackingservo of the optical pickup 3 is prevented.

However, in the case of a long High-level period of the defect signal ordepending on an error in the output of the held focus drive signal andtracking drive signal, the optical pickup 3 is displaced substantiallyfrom an original servo control position when the level of the defectsignal returns to Low.

Japanese Patent Laid-Open No. Sho 59-203276, for example, discloses amethod for preventing such displacement which, directing attention tocharacteristics of the TE signal such as periodicity, generates a pseudoerror signal approximating an original TE signal by calculation using atracking error and a track period, and uses the calculated pseudo errorsignal instead of the original TE signal while the level of the defectsignal is High.

Also, Japanese Patent Laid-Open No. Sho 64-39638 discloses a methodwhich changes focus offset adjusting voltage to a predetermined value tothereby prevent displacement of a focus coil while the level of thedefect signal is High, and thus minimizes the error when the level ofthe defect signal returns to Low.

The conventional techniques described above are all principally aimed toreduce a range of the control error while the level of the defect signalis High and after the level of the defect signal returns to Low, andgive no consideration to reduction of a period from the return to Low ofthe level of the defect signal to the return to a normal control stateof the servo.

In general, as the High-level period of the defect signal becomeslonger, the control error tends to be increased. Hence, in case wherethe control error is large if not departing from a normal servo controlrange when the level of the defect signal returns to Low, for example,as shown in FIGS. 3A, 3B, 3C, 3D, and 3E, the servo continues to beunstable and requires considerable time before the servo returns to anormal control state.

In order to return the servo quickly to the normal control state, thereis known a method which maintains a servo loop gain at ahigher-than-normal level immediately after a track jump or the like.However, when the servo loop gain is high, the servo is generally toosensitive to a defect such as a flaw on the optical disk. Therefore, themethod of increasing the servo loop gain cannot be used to improvedefect passage characteristics.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above, and it isaccordingly an object of the present invention to reduce time requiredfor the servo to return to the normal control state after the level ofthe defect signal returns to Low.

According to the present invention, there is provided a playbackapparatus comprising: RF signal generating means for generating an RFsignal on the basis of an analog signal outputted by an optical pickup;data signal generating means for generating a data signal by binarizingthe RF signal; defect signal generating means for generating a defectsignal for indicating a defect on a disk medium on the basis of the RFsignal; focus error signal generating means for generating a focus errorsignal on the basis of the analog signal outputted by the opticalpickup; a focus servo control means for controlling a focus servo of theoptical pickup in response to the focus error signal; tracking errorsignal generating means for generating a tracking error signal on thebasis of the analog signal outputted by the optical pickup; trackingservo control means for controlling a tracking servo of the opticalpickup in response to the tracking error signal; monitoring means formonitoring the defect signal and thereby detecting a start and an end ofa defect period; defect period processing control means for controllingthe focus servo control means and the tracking servo control means sothat the focus servo control means and the tracking servo control meansperform defect period processing when a result of the monitoring by themonitoring means indicates the defect period; and post-defect periodprocessing control means for controlling the focus servo control meansand the tracking servo control means so that the focus servo controlmeans and the tracking servo control means perform post-defect periodprocessing when a result of the monitoring by the monitoring meansindicates the end of the defect period.

The defect period processing control means can control the focus servocontrol means and the tracking servo control means so that the focuserror signal or the tracking error signal of the optical pickup is heldat a predetermined value.

The post-defect period processing control means can control the focusservo control means and the tracking servo control means so that servooperation of the optical pickup is sped up.

When the monitoring means detects the start of the defect period duringthe post-defect period processing performed under control of thepost-defect period processing control means, the post-defect periodprocessing control means can stop the post-defect period processing, andthe defect period processing control means can start the defect periodprocessing.

According to the present invention, there is provided a playback methodcomprising: an RF signal generating step for generating an RF signal onthe basis of an analog signal outputted by an optical pickup; a datasignal generating step for generating a data signal by binarizing the RFsignal; a defect signal generating step for generating a defect signalfor indicating a defect on a disk medium on the basis of the RF signal;a focus error signal generating step for generating a focus error signalon the basis of the analog signal outputted by the optical pickup; afocus servo control step for controlling a focus servo of the opticalpickup in response to the focus error signal; a tracking error signalgenerating step for generating a tracking error signal on the basis ofthe analog signal outputted by the optical pickup; a tracking servocontrol step for controlling a tracking servo of the optical pickup inresponse to the tracking error signal; a monitoring step for monitoringthe defect signal and thereby detecting a start and an end of a defectperiod; a defect period processing control step for controllingprocessing of the focus servo control step and processing of thetracking servo control step so that defect period processing isperformed when a result of the monitoring by processing of themonitoring step indicates the defect period; and a post-defect periodprocessing control step for controlling the processing of the focusservo control step and the processing of the tracking servo control stepso that post-defect period processing is performed when a result of themonitoring by the processing of the monitoring step indicates the end ofthe defect period.

According to the present invention, there is provided a program on arecording medium, comprising: an RF signal generating step forgenerating an RF signal on the basis of an analog signal outputted by anoptical pickup; a data signal generating step for generating a datasignal by binarizing the RF signal; a defect signal generating step forgenerating a defect signal for indicating a defect on a disk medium onthe basis of the RF signal; a focus error signal generating step forgenerating a focus error signal on the basis of the analog signaloutputted by the optical pickup; a focus servo control step forcontrolling a focus servo of the optical pickup in response to the focuserror signal; a tracking error signal generating step for generating atracking error signal on the basis of the analog signal outputted by theoptical pickup; a tracking servo control step for controlling a trackingservo of the optical pickup in response to the tracking error signal; amonitoring step for monitoring the defect signal and thereby detecting astart and an end of a defect period; a defect period processing controlstep for controlling processing of the focus servo control step andprocessing of the tracking servo control step so that defect periodprocessing is performed when a result of the monitoring by processing ofthe monitoring step indicates the defect period; and a post-defectperiod processing control step for controlling the processing of thefocus servo control step and the processing of the tracking servocontrol step so that post-defect period processing is performed when aresult of the monitoring by the processing of the monitoring stepindicates the end of the defect period.

The playback apparatus and method and the program on a recording mediumaccording to the present invention generate an RF signal on the basis ofan analog signal outputted by an optical pickup, generate a data signalby binarizing the RF signal, and generate a defect signal for indicatinga defect on a disk medium on the basis of the RF signal. Also, theplayback apparatus and method and the program on a recording mediumaccording to the present invention generate a focus error signal on thebasis of the analog signal outputted by the optical pickup, and controla focus servo of the optical pickup in response to the focus errorsignal. In addition, the playback apparatus and method and the programon a recording medium according to the present invention generate atracking error signal on the basis of the analog signal outputted by theoptical pickup, and control a tracking servo of the optical pickup inresponse to the tracking error signal. Furthermore, the playbackapparatus and method and the program on a recording medium according tothe present invention detect a start and an end of a defect period bymonitoring the defect signal, perform defect period processing when aresult of the monitoring indicates the defect period, and performpost-defect period processing when a result of the monitoring indicatesthe end of the defect period.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a configuration of a conventionaloptical disk playback apparatus;

FIGS. 2A, 2B, 2C, 2D, 2E, and 2F are diagrams of assistance inexplaining conventional processing for handling a defect;

FIGS. 3A, 3B, 3C, 3D, and 3E are diagrams of assistance in explainingconventional processing for handling a defect;

FIG. 4 is a block diagram showing a configuration of an optical diskplayback apparatus according to an embodiment of the present invention;

FIG. 5 is a flowchart of assistance in explaining defect handlingprocessing by the optical disk playback apparatus;

FIGS. 6A, 6B, 6C, 6D, and 6E are diagrams of assistance in explainingdefect handling processing by the optical disk playback apparatus;

FIGS. 7A, 7B, 7C, 7D, and 7E are diagrams of assistance in explainingdefect handling processing by the optical disk playback apparatus;

FIGS. 8A, 8B, 8C, 8D, and 8E are diagrams of assistance in explainingdefect handling processing by the optical disk playback apparatus;

FIGS. 9A, 9B, 9C, 9D, and 9E are diagrams of assistance in explainingdefect handling processing by the optical disk playback apparatus;

FIGS. 10A, 10B, 10C, 10D, and 10E are diagrams of assistance inexplaining defect handling processing by the optical disk playbackapparatus; and

FIGS. 11A, 11B, 11C, 11D, and 11E are diagrams of assistance inexplaining defect handling processing by the optical disk playbackapparatus.

DETAILED DESCRIPTION OF THE PREFFERED EMBODIMENTS

An example of configuration of an optical disk playback apparatus towhich the present invention is applied will be described with referenceto FIG. 4.

A spindle motor 22 forming the optical disk playback apparatus 20 drivesand rotates an optical disk 21. An optical pickup 23 irradiates theoptical disk 21 with laser light, generates a signal corresponding tothe reflected light, and then outputs the signal to an RF signalgenerating unit 24, an FE signal generating unit 25, and a TE signalgenerating unit 26. Also, the optical pickup 23 adjusts focus servooperation in response to a focus drive signal from a focus driver 39,and adjusts tracking servo operation in response to a tracking drivesignal from a tracking driver 46.

The RF signal generating unit 24 generates an RF signal corresponding tothe signal from the optical pickup 23, and then outputs the RF signal toa binarizing unit 27 and a defect processing control unit 28. The FEsignal generating unit 25 generates an FE signal on the basis of thesignal from the optical pickup 23, and then outputs the FE signal to afocus servo control unit 33. The TE signal generating unit 26 generatesa TE signal on the basis of the signal from the optical pickup 23, andthen outputs the TE signal to a tracking servo control unit 40.

The binarizing unit 27 converts the RF signal from the RF signalgenerating unit 24 into digital data of 0 or 1, thus generating a datasignal.

A defect detecting unit 29 forming the defect processing control unit 28detects a loss of a signal (defect) resulting from a flaw, a stain orthe like present on the optical disk 21 on the basis of a result ofcomparison between level of the RF signal from the RF signal generatingunit 24 and a predetermined threshold value, for example. The defectdetecting unit 29 generates a defect signal that has a Low level duringa normal period (not a period of a defect) and has a High level during adefect period. The defect detecting unit 29 outputs the defect signal toa defect period monitoring unit 30.

The defect period monitoring unit 30 monitors the defect signal from thedefect detecting unit 29. During a period in which the defect signal hasa High level, the defect period monitoring unit 30 generates a defectperiod signal indicating the High level of the defect signal, and thenoutputs the defect period signal to a defect period processing controlunit 31. When the level of the defect signal has returned from High toLow, the defect period monitoring unit 30 generates a defect period endsignal indicating that the level of the defect signal has returned fromHigh to Low, and then outputs the defect period end signal to apost-defect period processing control unit 32.

In response to the defect period signal from the defect periodmonitoring unit 30, the defect period processing control unit 31controls a pre-stage switch 34 and an FE signal previous value hold unit37 of the focus servo control unit 33, as well as a pre-stage switch 41and a TE signal previous value hold unit 44 of the tracking servocontrol unit 40.

In response to the defect period end signal from the defect periodmonitoring unit 30, the post-defect period processing control unit 32controls a post-stage switch 36 of the focus servo control unit 33, aswell as a post-stage switch 43 of the tracking servo control unit 40.

In the focus servo control unit 33, the FE signal from the FE signalgenerating unit 25 is supplied to the pre-stage switch 34, the FE signalprevious value hold unit 37, and a post-defect servo control unit 38.

The pre-stage switch 34 performs switching under control of the defectperiod processing control unit 31. When the pre-stage switch 34 isturned to a terminal (a) side, the FE signal from the FE signalgenerating unit 25 is outputted to a normal servo loop filter unit 35.On the other hand, when the pre-stage switch 34 is turned to a terminal(b) side, an FE signal held by the FE signal previous value hold unit 37is outputted to the normal servo loop filter unit 35. Normally, thepre-stage switch 34 is turned to the terminal (a) side.

The normal servo loop filter unit 35 generates a focus drive controlsignal by subjecting the FE signal inputted thereto via the pre-stageswitch 34 to low-frequency boost processing, phase compensationprocessing, low-pass filter processing and the like. The normal servoloop filter unit 35 then outputs the focus drive control signal to aterminal (b) side of the post-stage switch 36.

The post-stage switch 36 performs switching under control of thepost-defect period processing control unit 32. When the post-stageswitch 36 is turned to a terminal (a) side, a focus drive control signalfrom the post-defect servo control unit 38 is outputted to the focusdriver 39. On the other hand, when the post-stage switch 36 is turned toa terminal (b) side, the focus drive control signal from the normalservo loop filter unit 35 is outputted to the focus driver 39. Normally,the post-stage switch 36 is turned to the terminal (b) side.

Under control of the defect period processing control unit 31, the FEsignal previous value hold unit 37 holds the level of the FE signal fromthe FE signal generating unit 25, and then outputs the level of the FEsignal to the terminal (b) side of the pre-stage switch 34.

The post-defect servo control unit 38 generates a focus drive controlsignal by subjecting the FE signal from the FE signal generating unit 25to gain increase processing in addition to the processing of the normalservo loop filter unit 35. The post-defect servo control unit 38 thenoutputs the focus drive control signal to the terminal (a) side of thepost-stage switch 36.

The focus driver 39 generates a focus drive signal on the basis of thefocus drive control signal from the post-stage switch 36, and thenoutputs the focus drive signal to the optical pickup 23.

In the tracking servo control unit 40, the TE signal from the TE signalgenerating unit 26 is supplied to the pre-stage switch 41, the TE signalprevious value hold unit 44, and a post-defect servo control unit 45.

The pre-stage switch 41 performs switching under control of the defectperiod processing control unit 31. When the pre-stage switch 41 isturned to a terminal (a) side, the TE signal from the TE signalgenerating unit 26 is outputted to a normal servo loop filter unit 42.On the other hand, when the pre-stage switch 41 is turned to a terminal(b) side, a TE signal held by the TE signal previous value hold unit 44is outputted to the normal servo loop filter unit 42. Normally, thepre-stage switch 41 is turned to the terminal (a) side.

The normal servo loop filter unit 42 generates a tracking drive controlsignal by subjecting the TE signal inputted thereto via the pre-stageswitch 41 to low-frequency boost processing, phase compensationprocessing, low-pass filter processing and the like. The normal servoloop filter unit 42 then outputs the tracking drive control signal to aterminal (b) side of the post-stage switch 43.

The post-stage switch 43 performs switching under control of thepost-defect period processing control unit 32. When the post-stageswitch 43 is turned to a terminal (a) side, a tracking drive controlsignal from the post-defect servo control unit 45 is outputted to thetracking driver 46. On the other hand, when the post-stage switch 43 isturned to a terminal (b) side, the tracking drive control signal fromthe normal servo loop filter unit 42 is outputted to the tracking driver46. Normally, the post-stage switch 43 is turned to the terminal (b)side.

Under control of the defect period processing control unit 31, the TEsignal previous value hold unit 44 holds the level of the TE signal fromthe TE signal generating unit 26, and then outputs the level of the TEsignal to the terminal (b) side of the pre-stage switch 41.

The post-defect servo control unit 45 generates a tracking drive controlsignal by subjecting the TE signal from the TE signal generating unit 26to gain increase processing in addition to the processing of the normalservo loop filter unit 42. The post-defect servo control unit 45 thenoutputs the tracking drive control signal to the terminal (a) side ofthe post-stage switch 43.

The tracking driver 46 generates a tracking drive signal on the basis ofthe tracking drive control signal from the post-stage switch 43, andthen outputs the tracking drive signal to the optical pickup 23.

A control unit 50 controls a drive 51 to read a control program storedon a magnetic disk 52, an optical disk 53, a magneto-optical disk 54, ora semiconductor memory 55, and then controls the whole of the opticaldisk playback apparatus 20 on the basis of the read control program.

Defect handling processing by the optical disk playback apparatus 20will next be described with reference to a flowchart of FIG. 5 and FIGS.6A, 6B, 6C, 6D, and 6E. The defect handling processing is intended tohandle a loss of a signal (defect) resulting from a flaw, a stain or thelike present on the optical disk 21, and is started simultaneously witha start of processing of reproducing data from the optical disk 21.

At a step S1, the defect period processing control unit 31 of the defectprocessing control unit 28 effects control to turn the pre-stage switch34 of the focus servo control unit 33 and the pre-stage switch 41 of thetracking servo control unit 40 to the terminal (a) side, which is anormal position.

At a step S2, the defect period monitoring unit 30 of the defectprocessing control unit 28 monitors the defect signal from the defectdetecting unit 29 and stands by until the defect period monitoring unit30 detects the start of a defect period, that is, the defect periodmonitoring unit 30 detects a change in the level of the defect signalfrom Low to High, as shown in FIG. 6A. When the defect period monitoringunit 30 detects the start of a defect period (Td in FIG. 6A), theprocessing proceeds to a step S3.

At the step S3, the defect period monitoring unit 30 generates a defectperiod signal, and then outputs the defect period signal to the defectperiod processing control unit 31. In response to the defect periodsignal from the defect period monitoring unit 30, the defect periodprocessing control unit 31 controls the pre-stage switch 34 and the FEsignal previous value hold unit 37 of the focus servo control unit 33,as well as the pre-stage switch 41 and the TE signal previous value holdunit 44 of the tracking servo control unit 40, as processing during adefect period.

Under control of the defect period processing control unit 31, the FEsignal previous value hold unit 37 holds the level of an FE signalinputted from the FE signal generating unit 25 immediately before thedefect period Td, as shown in FIG. 6B, and then outputs the level of theFE signal to the terminal (b) side of the pre-stage switch 34. The TEsignal previous value hold unit 44 holds the level of a TE signalinputted from the TE signal generating unit 26 immediately before thedefect period Td, as shown in FIG. 6D, and then outputs the level of theTE signal to the terminal (b) side of the pre-stage switch 41. Thepre-stage switches 34 and 41 are turned to the terminal (b) side.

At a step S4, the defect period monitoring unit 30 monitors the defectsignal from the defect detecting unit 29 and stands by until the defectperiod monitoring unit 30 detects the end of the defect period, that is,the defect period monitoring unit 30 detects a change in the level ofthe defect signal from High to Low, as shown in FIG. 6A.

Thus, during the defect period Td, the FE signal held by the FE signalprevious value hold unit 37 is supplied to the normal servo loop filterunit 35, while the TE signal held by the TE signal previous value holdunit 44 is supplied to the normal servo loop filter unit 42.

Hence, during the defect period Td, the focus drive control signalgenerated by the normal servo loop filter unit 35 on the basis of the FEsignal is also held constant, and accordingly the focus drive signalgenerated by the focus driver 39 on the basis of the focus drive controlsignal is also held constant, as shown in FIG. 6C. In addition, thetracking drive control signal generated by the normal servo loop filterunit 42 on the basis of the TE signal is also held constant, andaccordingly the tracking drive signal generated by the tracking driver46 on the basis of the tracking drive control signal is also heldconstant, as shown in FIG. 6E.

Thus, during the defect period Td, a focus coil and a tracking coilwithin the optical pickup 23 are held at a position immediately beforethe defect period Td.

When the defect period monitoring unit 30 detects the end of the defectperiod (Td in the figure) at the step S4, the processing proceeds to astep S5.

At the step S5, the defect period monitoring unit 30 generates a defectperiod end signal and then outputs the defect period end signal to thepost-defect period processing control unit 32. In response to the defectperiod end signal from the defect period monitoring unit 30, thepost-defect period processing control unit 32 controls the post-stageswitch 36 of the focus servo control unit 33, as well as the post-stageswitch 43 of the tracking servo control unit 40, as processing after thedefect period. Ta in FIGS. 6A, 6B, 6C, 6D, and 6E denotes a periodduring which the post-defect period processing is performed.

Under control of the post-defect period processing control unit 32, thepost-stage switches 36 and 43 are turned to the terminal (a) side. Thus,immediately after the defect period Td, a focus drive control signalwith an increased servo gain from the post-defect servo control unit 38is supplied to the focus driver 39, while a tracking drive controlsignal with an increased servo gain from the post-defect servo controlunit 45 is supplied to the tracking driver 46.

At a step S6, the defect period monitoring unit 30 determines whetherthe defect signal is brought into a defect state again. When the defectperiod monitoring unit 30 determines that the defect signal is broughtinto a defect state again, the post-defect period processing is stoppedimmediately, and the processing returns to the step S3 to repeat theprocesses from the step S3 on down. When the defect period monitoringunit 30 determines at the step S6 that the defect signal is not broughtinto a defect state again, the processing proceeds to a step S7.

At the step S7, whether the post-defect period processing is to be endedor not is determined on the basis of whether a predetermined condition(to be described later) is satisfied. The processing at the steps S6 andS7 is repeated until it is determined that the post-defect periodprocessing is to be ended. When it is determined at the step S7 that thepost-defect period processing is to be ended, the post-stage switches 36and 43 are turned to the terminal (b) side. Then, the processing returnsto the step S2 to repeat the processes from the step S2 on down.

The conditions for turning the post-stage switches 36 and 43 to theterminal (b) side, that is, the conditions for timing of ending theperiod Ta are: passage of a predetermined time after turning thepost-stage switches 36 and 43 to the terminal (a) side; the passing of areference level by the FE signal and the TE signal; and reoccurrence ofa defect state. The post-stage switches 36 and 43 are turned to theterminal (b) side when one of the conditions is satisfied.

As described above, according to the defect handling processing by theoptical disk playback apparatus 20, the post-defect period processing,in which an action for correcting servo displacement is produced morestrongly than during a normal period (a period of no defect), is startedimmediately after detection of the end of the defect period Td.Therefore, servo displacement can be corrected quickly as compared witha case (FIGS. 3A, 3B, 3C, 3D, and 3E) where the post-defect periodprocessing is not performed.

Incidentally, the turning of the pre-stage switches 34 and 41 while thepost-defect period processing is performed at the step S5 is notdetermined uniquely because the turning of the pre-stage switches 34 and41 is changed depending on the method of the post-defect periodprocessing and a situation in which a defect state occurs again.

The above-described operation of the post-defect servo control unit 38of the focus servo control unit 33 and the post-defect servo controlunit 45 of the tracking servo control unit 40 will hereinafter bedescribed as first operation.

The post-defect servo control unit 38 of the focus servo control unit 33may detect a difference between the level of the FE signal immediatelyafter the end of the defect period and a reference level and output apulse voltage acting to reduce the difference to the terminal (a) of thepost-stage switch 36 as a focus drive control signal.

Similarly, the post-defect servo control unit 45 of the tracking servocontrol unit 40 may detect a difference between the level of the TEsignal immediately after the end of the defect period and a referencelevel and output a pulse voltage acting to reduce the difference to theterminal (a) of the post-stage switch 43 as a tracking drive controlsignal. Such operation of the post-defect servo control units 38 and 45will hereinafter be described as second operation.

When the post-defect servo control units 38 and 45 perform the secondoperation, the condition for timing of returning the post-stage switches36 and 43 to the terminal (b) side, that is, the condition for timing ofending the period Ta for performing the post-defect period processing isthe passing of a reference level by the FE signal and the TE signal.

FIGS. 7A, 7B, 7C, 7D, and 7E show a result of defect handling processingwhen the post-defect servo control units 38 and 45 perform the secondoperation.

FIGS. 8A, 8B, 8C, 8D, and 8E show a result of processing when arelatively short defect occurs three times during the performance of thepost-defect period processing in which the post-defect servo controlunits 38 and 45 perform the first operation.

FIGS. 9A, 9B, 9C, 9D, and 9E show a result of processing when arelatively short defect occurs three times during the performance of thepost-defect period processing in which the post-defect servo controlunits 38 and 45 perform the second operation.

Since the servo is in a more unstable state during the post-defectperiod processing than during normal operation, the level of the focusdrive signal and the tracking drive signal held immediately afterreoccurrence of a defect state may not necessarily be appropriate.

Therefore, when a defect state occurs, output voltage of the focus drivesignal and the tracking drive signal may be fixed at a reference level(for example zero potential) so that voltage is not applied to the focuscoil and the tracking coil.

In such a case, by resetting the length of the period Ta to an initialvalue, it is possible to prevent the post-defect period processing frombeing ended within less than a specified time. It is also possible todeal with a case where a defect state continually occurs in a shorttime.

FIGS. 10A, 10B, 10C, 10D, and 10E show a result of processing where theoutput voltage of the focus drive signal and the tracking drive signalis set to be fixed at a reference level when a defect state occurs, anda relatively short defect occurs three times during the performance ofthe post-defect period processing in which the post-defect servo controlunits 38 and 45 perform the first operation.

FIGS. 11A, 11B, 11C, 11D, and 11E show a result of processing where theoutput voltage of the focus drive signal and the tracking drive signalis set to be fixed at a reference level when a defect state occurs, anda relatively short defect occurs three times during the performance ofthe post-defect period processing in which the post-defect servo controlunits 38 and 45 perform the second operation.

As described above, the optical disk playback apparatus 20 to which thepresent invention is applied monitors reoccurrence of a defect, and whena defect occurs, the optical disk playback apparatus 20 stops thepost-defect period processing to perform defect processing again.Therefore, it is possible to solve the problem of the servo becoming toosensitive to a defect such as a flaw when the loop gain of the servo isincreased, and it is thereby possible to make the servo less affected bya defect even when the servo loop gain is high.

It is to be noted that the present invention can be applied not only toplayback apparatus such as the present embodiment for playing back anoptical disk such as a CD (Compact Disc) but also to playback apparatusfor playing back a DVD (Digital Versatile Disc), an MD (Mini Disc), amagneto-optical disk and the like.

The series of processing steps described above may be carried out notonly by hardware but also by software. When the series of processingsteps is to be carried out by software, a program is installed from arecording medium onto a computer where programs forming the software areincorporated in dedicated hardware, or a general-purpose personalcomputer that can perform various functions by installing variousprograms thereon, for example.

Examples of the recording medium include not only program-recordedpackage media distributed to users to provide the program separatelyfrom computers, such as the magnetic disks 52 (including a floppy disk),the optical disks 53 (including CD-ROM (Compact Disk-Read Only Memory)and DVD (Digital Versatile Disk)), the magneto-optical disks 54(including MD (Mini Disk)), or the semiconductor memories 55, as shownin FIG. 4, but also a ROM and a hard disk storing the program andsupplied to a user in a state of being preincorporated in a computer.

It is to be noted that in the present specification, the stepsdescribing the program recorded on a recording medium include not onlyprocessing steps carried out in time series in the described order butalso processing steps carried out in parallel or individually and notnecessarily in time series.

As described above, the playback apparatus and method and the program ona recording medium according to the present invention detect the startand the end of a defect period by monitoring a defect signal, performdefect period processing when a result of the monitoring indicates adefect period, and perform post-defect period processing when a resultof the monitoring indicates the end of the defect period. Therefore, itis possible to reduce time required for the servo of an optical pickupto return to a normal control state after the end of a defect period.

1. A playback apparatus for reproducing data recorded on a disk mediumby using an optical pickup, said playback apparatus comprising: RFsignal generating means for generating an RF signal on the basis of ananalog signal outputted by said optical pickup; data signal generatingmeans for generating a data signal by binarizing said RF signal; defectsignal generating means for generating a defect signal for indicating adefect on said disk medium on the basis of said RF signal; focus errorsignal generating means for generating a focus error signal on the basisof said analog signal outputted by said optical pickup; focus servocontrol means for controlling a focus servo of said optical pickup inresponse to said focus error signal; tracking error signal generatingmeans for generating a tracking error signal on the basis of said analogsignal outputted by said optical pickup; tracking servo control meansfor controlling a tracking servo of said optical pickup in response tosaid tracking error signal; monitoring means for monitoring said defectsignal and thereby detecting a start and an end of a defect period;defect period processing control means for controlling said focus servocontrol means and said tracking servo control means so that said focusservo control means and said tracking servo control means perform defectperiod processing when a result of the monitoring by said monitoringmeans indicates said defect period, wherein the defect period processingincludes controlling said focus servo control means and said trackingservo control means so that at least one of said focus servo and saidtracking servo is not energized; and post-defect period processingcontrol means for controlling said focus servo control means and saidtracking servo control means so that said focus servo control means andsaid tracking servo control means perform post-defect period processingwhen a result of the monitoring by said monitoring means indicates theend of said defect period, wherein said post-defect period processingcontrol means includes a resetting means for resetting the length of thepost-defect period processing to an initial value to prevent thepost-defect period processing from being ended within less than aspecified time.
 2. A playback apparatus as claimed in claim 1, whereinwhen said monitoring means detects the start of said defect periodduring said post-defect period processing performed under control ofsaid post-defect period processing control means, said post-defectperiod processing control means stops said post-defect periodprocessing, and said defect period processing control means starts saiddefect period processing.
 3. A playback apparatus as claimed in claim 1,further comprising a focus error signal previous value hold unit to holdthe focus error signal at a previous value during the defect periodprocessing.
 4. A playback apparatus as claimed in claim 1, furthercomprising a first post-defect servo control unit to drive the focusservo of the optical pickup with an increased servo gain.
 5. A playbackapparatus as claimed in claim 1, further comprising a tracking errorsignal previous value hold unit to hold the tracking error signal at aprevious value during the defect period processing.
 6. A playbackapparatus as claimed in claim 1, further comprising a second post-defectservo control unit to drive the tracking servo of the optical pickupwith an increased servo gain.
 7. A playback method for a playbackapparatus to reproduce data recorded on a disk medium by using anoptical pickup, the method comprising: an RF signal generating step forgenerating an RF signal on the basis of an analog signal outputted bysaid optical pickup; a data signal generating step for generating a datasignal by binarizing said RF signal; a defect signal generating step forgenerating a defect signal for indicating a defect on said disk mediumon the basis of said RF signal; a focus error signal generating step forgenerating a focus error signal on the basis of said analog signaloutputted by said optical pickup; a focus servo control step forcontrolling a focus servo of said optical pickup in response to saidfocus error signal; a tracking error signal generating step forgenerating a tracking error signal on the basis of said analog signaloutputted by said optical pickup; a tracking servo control step forcontrolling a tracking servo of said optical pickup in response to saidtracking error signal; a monitoring step for monitoring said defectsignal and thereby detecting a start and an end of a defect period; adefect period processing control step for controlling processing of saidfocus servo control step and processing of said tracking servo controlstep so that defect period processing is performed when a result of themonitoring by processing of said monitoring step indicates said defectperiod, wherein the defect period processing includes controlling saidfocus servo control step and said tracking servo control step so that atleast one of said focus servo and said tracking servo is not energized;and a post-defect period processing control step for controlling theprocessing of said focus servo control step and the processing of saidtracking servo control step so that post-defect period processing isperformed when a result of the monitoring by the processing of saidmonitoring step indicates the end of said defect period, wherein saidpost-defect period processing control step includes resetting the lengthof the post-defect period processing to an initial value to prevent thepost-defect period processing from being ended within less than aspecified time.